ML19352A003
| ML19352A003 | |
| Person / Time | |
|---|---|
| Site: | Summer  |
| Issue date: | 02/20/1981 |
| From: | Nichols T SOUTH CAROLINA ELECTRIC & GAS CO. |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8102250359 | |
| Download: ML19352A003 (4) | |
Text
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SOUTH CAROLINA ELECTRIC a gas COMPANY POST OF FICE BOX 764 CotuMs A, SOUTH CAnOLIN A 29218 T. C. NicHOLs. J n.
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February 20, 1981 Nuctcan Onnario=s -
1
~i Mr.-' Harold R. Denton, Director Office of Nuclear Reactor Regulation U.
S. Nuclear Regulatory Commission l
Washington,'D. C. 20555 Subj ect: Virgil C. Summer Nuclear Station
.l Docket No. 50/395 Load Sequencer
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Dear Mr. Denton:
In the Safety Evaluation Report outstanding issue number 1.6.9 involves the load sequencer. This letter provides a copy of an FSAR change which with the existing FSAR material completes the " design description" item.
It should be noted that the " reliability analysis" was previously-delivered in person to Mr. Om Chopra and our February 4, 1981 letter provided our position on the " sneak circuit analysis".
We request that this caterial be reviewed as soon as possible.
If you have any questions, please let us know.
l Very truly yours,
,/
4 f
T. C. Nichols, Jr.
RBC:TCN:rh t
cc:
V. C. Summer A. A. Smith G. H. Fischer H. N. Cyrus T. C. Nichols, Jr.
J. B. Knotts, Jr.
E. H. Crews,-Jr.
J. L. Skolds
.O. W. Dixon, Jr.
B. A. Bursey C. A. Price O._S. Bradham D.-A.
Nauman ISEC.
W. A.-Williams, Jr.
.NPCF/Whitaker R. B.-Clary File A. R. Koon 3
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3.
Diesel start (see Chapter 8).
4.
Feedwater isolation (see Chapter 10).
5.
Ventilation isolation valve and damper actuators (see Chapter 6),
b 6.
Steam line isolation valve actuators (see Chapter 10).
7.
Reactor building spray pump and valve actuators (see Chapter 6).
I 8.
ESF loading sequence (see Section 7.3.1.1.5).
l If an accident is assumed to occur coincident with a loss of offsite power, the engineered safety features loads must be sequenced onto the diesel generators to prevent overloading them. This sequence is dis-cussed in Chapter 8.
The design meets the requirements of Criterion 35 of the 1971 GDC.
~7.3.1.1.5 Engineered Safety Features Loading Sequence Control Fanels THs ee r &
m ~ F? % - r f e.:_:
d:: caricu- ::nditiene o f h e eef=effaitc_pc=r, g
,degend;ti n of ecitage, 2nd/;r i.f% injection. The loss of offsite i
power or degradation of voltage considered here is related to the engi-19 neered safety features buses (7.2 kv buses IDA and/or IDB). Loss of
_l-voltage is detected on either bus by 3/3 loss of voltage relays.
Degraded voltage is-detected oneither bus by 3/3 degraded voltage
' relays. The safety injection signal'is generated by the solid-state s'P
'Imur protection system.p When initiated, the sequence provides timing to load.
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the buses at five second intervals.
Order of loading is determined by system requirements, design capabilities of the diesel and the type of incident or-accident, as evaluated by the ESFLS logic circuitry (see Figure 7.3-1 and Section 8.3).
In addition, the sequence provides for 7
I tripping and blocking of loads. The ESFLS is located in the relay room
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and indication is provided on the main control board.
It provides
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7.3-8 MENDMENTjI9
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O are established, closes the emergency power source circuit bicaker.
In the case of_a safety injection signal and/or ESF bus undervoltage, the j
ESF loading sequencer (see Section 7.3.1 for a detailed discussion) trips selected bus loads including all non-class 1E loads. The bus is then reloaded in the sequence shown in Table 8.3-3.
Items indicated by zero second loading sequence in Table 8.3-3 are not tripped and, there-fore, are-immediately loaded when the emergency power source circuit breaker is closed. All other. required loads are loaded in sequence by y
the ESF-loading sequencer.
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"The 7.2KV ESF buses are each provided with the loss of voltage relays
[
set a approximately 80 percent of the nominal bus voltage level and 22 I
three degraded voltage relays set at 91.34 percent of the nominal bus voltage level.". Operation of three out of three of the loss of voltage relays, or three out of three of the degraded voltage relays initiates actuation of the ESF loading sequencer associated with the diesel gener-ator related to the affected bus..The logic for these controls is illu-strated in Figure 8.3-Oo.
A three second time lag of initiation of i
diesel generator start is provided to permit a momentary system voltage d.p caused by a transient or switching conditions. A seven second time lag from Diesel Generator start is provided to delay bus tripping there-21 f ore with the degraded voltage the maximum dead busX time is three
_ j t.y seconds as ' compared to the ten seconds dead bus time allowed for com-
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plete loss of off site power. When the diesel generators are started and loaded as a result _of an undervoltage condition, the ESF loading sequencer logic prevents further undervoltage tripping of the safety related loads. When the buses are returned to the offsite power 5
sources, the undervoltage tripping f ea'.ure is automatically reinstated'.
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Dse. r C Vf i
The emergency, diesel generators and normal station service are synchro-
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nized only during periodic testing.. Synchronizing capability is pro-vided to reconnect the' emergency. diesel generators to the offsite power network when voltage is restored subsequent to the loss of offsite 15 i -
power.. Synchronization is performed manually, when required. ESF
. equipment :is duplicated on separate 7200. volt and 480 volt (as a
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_ 8.3 AMENDMENT M 17O e(.
D V h he 6a) Le E% g Ab
INSERT A The ESFLS automatically loads engineered safety features components to the ESF buses under the following conditions:
a.
loss of offsite power or degradation of voltage b.
safety injection c.
safety injection coincident with loss of offsite power or degradation of voltage.
INSERT B To assure component operation under the various initiating conditions,
'two-initiating. sequences are provided.
These sequences are a " blackout sequence," which loads the components needed to shutdown the plant in the event of a loss-of power or degraded voltage, and a " safety injection sequence," which loads the components needed to mitigate the consequences of design bases accidents' occurring coincident with a loss of offsite
-power or degradation of voltage.
LThe' initiation of ESF loads following safety injection with ESF bus power
-available. utilizes-the.same " safety injection sequence" identified above.
Using.of.the loading sequencer during conditions when ESF bus power is available provides.the following benefits:
' l.-
enhanced reliability due.to a simplified logic for component actuation-2.
improved on line testing capability.
As' discussed in Section'8.3,-each 7.2 ESF bus is-fed'from both the normal
-i
-(offsite) and emergency (onsite) supplies and each ESF bus is-provided
.with: loss of voltageJand degraded voltage. relays.
This arrangement enables 1
- operation of1the-ESFLS' independent'of the source'_(offsite-or onsite).of power.
INSERT C
.TheLESFfloading sequencer' performs'under various conditions of loss of-
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offsite power,' degradation ^of voltage,z and/or safety injection.
For a
- detailed description'- of the -loading. sequencer, refer to Section 7. 3.1.1.5.
G FCN 280
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